1. Field of the Invention
The present invention relates to a method of forming a direct positive image and a silver halide photographic light-sensitive material by which direct positive photographic images are formed, and more particularly, to a photographic light-sensitive material, whose photographic emulsion layers or other hydrophilic colloid layers contain a novel compound as a fogging agent.
2. Description of the Prior Art
In the field of silver halide photography, a technique in which positive photographic images are obtained without going through negative images or intermediate processing producing negative images is called direct positive photography, and photographic light-sensitive materials and photographic emulsions using such a photographic technique are called direct positive light-sensitive materials and direct positive photographic emulsions, respectively.
A variety of direct positive photographic techniques are known. The most useful methods are methods in which silver halide grains which have previously been fogged are exposed to light in the presence of a desensitizer followed by development, and methods comprising exposing silver halide emulsion containing silver halide grains having light-sensitive specks mainly inside the silver halide grains to light and then developing the exposed emulsion in the presence of a fogging agent. The present invention relates to the latter technique. Silver halide emulsions possessing light-sensitive specks in the inside of the silver halide grains and forming latent images mainly inside the grains are referred to as an internal latent image type silver halide emulsions and thus distinguished from silver halide grains which form latent images mainly on the surface of the grains and referred to as surface latent image type silver halide grains.
A method for obtaining direct positive images by surface-developing an internal latent image type silver halide photographic emulsion in the presence of a fogging agent, and photographic emulsions employed for such a method are disclosed in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318 and 3,227,552. British Pat. Nos. 1,011,062 and 1,151,363, Japanese Pat. No. 29405/1968, etc.
In the internal latent image type method for obtaining direct positive images, the fogging agent can be incorporated into a developing solution, however, by incorporating the fogging agent into photographic emulsion layers or associated layers of the light-sensitive material and thereby adsorbing it onto the surface of the silver halide grains, better reversal characteristics can be obtained.
As fogging agents which are employed in the above-described methods for obtaining direct positive images, there are hydrazine and derivatives thereof as described in U.S. Pat. Nos. 2,563,785, 2,588,982 and 3,227,552, respectively. In particular, U.S. Pat. No. 3,227,552 discloses that hydrazide and hydrazine type compounds which are derivatives of hydrazine can be incorporated not only in developing solution but also in light-sensitive layers.
However, when hydrazine compounds are incorporated into the emulsion layer, the compounds must be employed in a considerably high concentration (e.g., about 2 g per 1 mol of silver), and in addition, because the fogging agent is transferred from the emulsion layer to the developing solution during development processing the concentration of the fogging agent in emulsion varies and unevenness in the maximum density results (at the non-exposed areas), i.e., the fogging effect becomes non-uniform, in the case of multilayer color light-sensitive material, among the emulsion layers.
Furthermore, it is known that these fogging agents evolve nitrogen gas during fogging. This gas gathers in a film to form gas bubbles, which sometimes imparts unexpected damage to photographic images.
In order to avoid these shortcomings, fogging agents comprising a heterocyclic quaternary salt compounds described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738 and 3,759,901, Japanese patent application (OPI) Nos. 3426/1977 and 69613/1977 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") have been used.
However, in most cases, sensitizing dyes are incorporated into the silver halide emulsion for spectral sensitization, and particularly in color light-sensitive materials, layers which are respectively sensitive to both green light and red light in addition to a layer sensitive to blue light are essentially required and emulsions in the green sensitive layer and red sensitive layer necessarily contain sensitizing dyes. In direct positive emulsions, where fogging agents are contained together with sensitizing dyes sensitive to green light and red light, competitive adsorption in the silver halide emulsion occurs between the sensitizing dyes and the quaternary salt fogging agent. If a fogging agent in an amount sufficient to form the fogging centers is incorporated into the emulsion, spectral sensitization is prevented. On the other hand, if a spectrally sensitizing dye in a concentration sufficient to obtain desired spectral sensitization is incorporated into the emulsion, the formation of the fogging center is prevented.
One means for overcoming this disadvantage, wherein a sensitizing dye having a nucleating substituent in the dye molecule is employed, is disclosed in U.S. Pat. No. 3,718,470.
However, when nucleating activity as well as spectrally sensitizing activity are simultaneously imparted to one molecule, the use of the dye in an appropriate amount for the spectral sensitization is insufficient for the nucleating activity, and on the other hand, the use of the dye in an amount sufficient for the nucleating activity is inappropriate for the spectral sensitization.
In addition, a disadvantage which is common to the hydrazine type compounds and heterocyclic quaternary salt compounds is their large temperature-dependency for the nucleating activity. That is, if the developing temperature is low, the lower is the nucleating activity, and if the developing temperature is high, the sensitivity is reduced.
In order to eliminate this disadvantage, it has been proposed in U.S. Pat. No. 4,030,925 (corresponding to German patent application (OLS) No. 2,635,316) and U.S. Pat. No. 4,031,127 (corresponding to German patent application (OLS) No. 2,635,317) that acyl hydrazinophenylthiourea compound be employed.
However, in this field of art, it has long been desired to develop more improved fogging agents having less temperature-dependency (upon processing) with direct positive system not only using the p-hydroxyarylsulfonamide type dye image-providing materials as described in the aforementioned U.S. patents but also using dye image-providing materials different therefrom.